Liquid level indicator



Patented May '16, 1939 LIQUID LEVEL INDICATOR Malcolm B.- Hall, Foxboro, Mass., assignor to The Foxboro Company, Foxboro, Mass., a corpora- 'tion of Massachusetts Application October 10, 1936, Serial No. 104,927

" s claims. (ci. ss-'atm This invention relates to an apparatus for measuring and recordingy liquid level.

In the present embodiment of the invention, the hydrostatic pressure of a body of liquid whose digester presents a difficult problem due to the corrosive and chemically active vnature of the sulphite liquor and also because of the high and varying pressures existing in the digester during 5 level is to be measured-is @taken at a reference the cooking operation. In the past try cocks level and is transmitted, by a barometric column, have been installed at various levels on the side i. e'. a column of liquid in a pipe sealed at the top of the digester to indicate the liquid level. But and open and exposed to pressure at the bottom, this means is unsatisfactory because of the obto pressurelsensitive mechanism such, for exnoxious character of the acid fumes that escape 1 0 ample, as a manometer and float arrangement. when the cocks are tried,

Properly calibrated, then, thev pressure-sensitive SOme digesters have been equipped With gauge mechanism translates hydrostatic pressure into glasses for level measurement purposes, but such liquid level. This provides a novel and convenient glaSSeSInl-lst alWaYS be mOllntedi n the Side 0f the method for measuring the level of a liquid at a dieester and, therefore, below the floor where point above and removed from the body of the the Operator WOIkS, thus making it necessary for liquid. I the cook to go to the floor below in order to make Since this 1eve1 measurement is affected by the his observations of the liquor level unless some y pressure on the surface of the liquid, if the sursystem 0f milIOl'S 01 signals is used- Further, face pressure varies, it is desirable to compensate not only do gauge glasses tend to foul and so 2 for )the ell'ect of the surface pressure by using a beoome inoperative, but also there is a decided differential-pressure measuring device, one side element 0f danger in the use 0f gauge glasses, for

of which is connected to the hydrostatic pressure they are relatively fragile. If One breaks, it perand the other side of which is` in communication mits the hot liquor and S02 gas t0 escape under with the surface pressure. 1f the 1iquid being Pressure into the dieester house- 25 measured is corrosive or chemically 'active' a It is another object of this invention, theresecond barometrlc column may be conveniently loro to provide an apparatus for Continuously used to provide a connection for transmitting the measuring the liquor level in a Sulplllte digestel', surface pressure to the differential-pressure .ami to provide simple and emoieut appal'atuS fol' 30 measuring device, such an arrangement also indicating and recording this liquor level measureprovides a means for compensating for `the presmolli' al; a desired point suoli as the Cooking oon' sure eaused by the weight of the liquid in the mst trol station. at the top of the digester, whereby the -column and'thus permits a zero indication on the many advantages ooouiiug i from accurate differential pressure measuring device at some knowledge of the liquor level ut all times may be 35 convenient liquid level. The two. barometric availed off e columns are preferably filled with a liquid that These and other apparent objeots and uddoes not have such chemical react-,ien with the vantages are obtained by the means described in uquia being measured as wcu1d interfere with the the following specification, and may be more operation of the measuring mechanism or its asreadily understood by Telefono@ lio the accompany' 4o sociated par-ts, This liquid prevents the corrosive lug drawing in which:

effect of the liquid being measured fromreeehi'ng Figure 1 illustrates apparatus, embodying the the measuring device and itself is chemically ininvention, applied t0 the t0!) 0f a slllphite diactive toward said measuring device so as not to gestor illustrated in part; und detrimentally attack the instrument. vFigure 2 shows a rear View of the differential- 45 Aceordinglit is an objeetof this invemienV pressure indicating andrecording instrument used to provide an improved apparatus for determin-` in this embodiment, with a portion thereof paring liquid level. tially cut away to show operating elements.

Apparatus incorporating an embodiment of the Referring to Figure 1, the upper Portion 0f a invention is particularly adapted to the problem sulphite digester is shown at I in` which the level 5o of measuring the liquor level in sulphite digesters, of the liquor is to be determined. The top 2 of in the operation of which accurate knowledge of the digester I extends up through the operating the level aids in the maintaining of those levels floor 3 of the dlgester house (not shown), from best suited for the production of the quality of which position the cooking operations are cuspulp desired. tomarily controlled. An instrument, generally 55 The measurement 0f liquor level in a sulphte indicated at I3, is also located above the floor 3 for indicating and recording the level in the digester.

'Ihe instrument is suitably connected with the hydrostatic pressure of the liquor in the digester. T this end a short pipe or drop leg 6 (lower part of Figure 1) is connected at its upper end to digester I at a point corresponding to the lower limit A of the range through which measurement of level is desired. The lower end of drop leg 8 is connected through an enlarged pipe or capacity chamber 1 to a pipe or drop leg 8 that extends up through floor 3 to a low-pressure chamber I2 of the differential-pressure indicating and recording instrument I3. Provided between the pipe 8 and the instrument is a valve 9 and air trap I0 for purposes to be described hereinafter.

The instrument is connected also with the surface or gas pressure above the liquor level. To this end a 'high-pressure chamber I4 of the instrument is similarly connected through pipe I5, air trap I8, valve I1 and pipe or drop leg I8, to the bottom of a horizontal condensing chamber I8. The chamber I9 is connected, preferably about half-way up, to the top of the digester I at some convenient point 2l by pipe 20 which slopes downwardly toward the digester. The low and high pressure chambers I2 and I4, and their respective piping, are connected respectively through pipes II and I5, valves 22 and 23, pipe 28, check-valve 28 and a hand valve 21 to a water supply pipe 24.

When the apparatus is in condition for operation, the drop legs 8 and I8 are filled with water from supply 24 to form two barometric columns. To accomplish this the valves 21, 22 and 9 are opened (keeping valves I1 and 23 closed) to admit water to fill the chamber I2, pipe I I, air trap Il, drop leg 8, capacity tank 1 and the short drop leg 8. Valve 9 is then closed and the air vent 33 on the top of the low pressure chamber I2 of the instrument I3 is open until water flows therefrom thus venting anyair or other gas which may have been trapped therein. y Vent 33 is then closed and the air vent 32 in the top of air trap I8 is opened until all the air trapped therein escapes and water flows out. 'I'he vent 32 is then closed and finally valve 22 is closed. In a similar manner valves 23 and I1 are opened (keeping valves 22 and 9 closed) and the high pressure chamber I4, pipe I5, air trap I8, drop leg I8 and part of the condensing chamber I9 are filled with water, valve I1 is closed, vent 33 in the top of chamber I4 and vent 32' in air trap I8 are respectively opened until water flows out and then closed, and finally the valve 23 i's closed. This procedure fills the entire system'with water and ensures the escape of air or other gas imprisoned therein, and, when the valves 9 and I1 are reopened, the apparatus is ready for operation.

'Ihe drop legs 8 and I8 thus become barometric legs with the instrument I3 measuring the differential pressure between their upper ends. The barometric columns 8 and- I8 also provide an effective seal between the instrument I3 and the -digester I, preventing the corrosive liquorin the digester from reaching the instrument. With this arrangement, seepage of the corrosive liquor into the drop legs is prevented from reaching the instrument by flushing the system, preferably after each cook, with fresh water from supply 24.4 'I'his may be accomplished simply by opening valve 22 to flush leg 8, and thenafter closing valve 22, opening valve 23 to flush leg I8. When the first operation is performed the differential gauge will indicate zero differential and when the second operationvis carried out it will indicate maximum differential. 'I'hus the record will show whether or not the system has been flushed.

v When filling the system the water flows intoA the condensing chamber I9 and flows out through pipe 2li until the flow is stopped. Thereafter it continues to drain out of pipel 20 until the level drops to the point 3l, at which time the lower portion of the chamber I9 remains filled up to the height of the outlet at point 3|. This condensing chamber I9 is so located with respect to t'he'digester I that the level of the water in the condensing chamber corresponds to the upper limit B of the range of level variation in the digester. The condensing chamber I9, being at a lower temperature than the digester I, also serves to condense vapors reaching it through the pipe 20 which then drain back through the pipe to the digester. g

The drop leg 6 is provided 4to prevent the water from running out of the drop leg 8 during operation and thereby destroying the effect of the barometric leg. It accomplishes this by acting as the usual short leg of a barometric column which prevents gas from entering the barometer tube and depressing the liquid column therein. condensing chamber I9 acts in a similar manner to prevent the water from running out o1' drop leg I8. In addition, drop leg 8 and condensing chamber I9 provide water seals between the dlgester I-and the instrument I3 in the event that the drop legs 8 and I8 are drained.

Because the tubing which would customarily be used for the pipes 8 and I8 in connecting instrument I3 to the digester usually is of small diameter, and because the volumes of the instrument chambers I2 and I4 may be relatively large as compared with the volumes of these pipes, the capacity chamber 1 is placed in pipeA 8 to provide sufficient water to keep pipe 8 full of water from the chamber 1 even when the liquid in leg 8 is pushed back to its farthest position when the liquor in the digester rises to its highest level, thereby preventing liquor in the digester from reaching chamber I2. Condensing chamber I9 functions similarly in connection with pipe I8.

It is desirable that pipe 28, condensing chamber I9, the drop leg 8 and capacity tank 1 all be lconstructed of acid-resisting material. The check valve 26 prevents waterin the legs or the instrument from backing up in the water supply 24 in the event of the pressure in the water main becoming less than the pressure in the digester during flushing operation.

Figure 2 shows a rear view of the differentialpressure indicating and recording instrument I3 with a portion thereof cut away in order that the operation of the device may be more readily understood. Such an instrument may be similar to that shown in U. S. Patent 1,808,207 to Lyman Cook, issued June 2, 1931. This device may be considered a U-tube mercury manometer provided with mechanism for measuring, indicating and recording the difference in the level of the mercury in the two sides of the manometer. For convenience, it may be described as comprising a low-pressure chamber I2 and a high-pressure chamber I4, connected by a U-tube 34 and filled with mercury to the proper level. The U-tube 34 is provided with check valves 35 in each leg thereof to prevent a sudden rush .of the mercury 'from'one chamber to the other, and also with a drain plug 38 for draining the mercury from the instrument when necessary.

Change of the level of the mercury in the high- 2,1. cavas Y mechanism which comprises a float I1 attached to an upright member ll which coacts with a segmental lever arm 39 rotatingon shaft Il. Ro-

tation of shaft Il positions a pen arm 4| (see Figure 1) with-respect to a rotating chart 42 in the customary manner. The twopressure chambers l2 and. are connected to the pressures whose differential is to be measured by the pipes II and I5, respectively, and are completely illled with water and to form the upper ends of the barometric legs l and Il.

In the embodiment shown, this instrument has a differential pressure; range at least equivalent to the hydrostatic pressure exerted by a column of the liquid being measured whose height is equal to the distance between the levels A and B. The pressure in the high-pressure hamber Il of the instrument il will be equal to tl e pressure on the top of the liquor minus the hydrostatic pressure exerted by av column of water of a height equal to the distance between the level B and a level M which is the mean level of the mercury in the two chambers of the diilerential instrument Il. As the height of this water column is approximately constant for any given installation, the pressure in the high-pressure chamber I4 will vary directly with the pressure in the top of the digester I. The pressure in the lchamber I2 will be equal to the pressure on the surface of the liquor plus the hydrostatic pressure exerted by a column of the iiuld of a height equal to the distance from Athe actual liquor level I-I to reference level A, minus the pressure exerted by the column the digester to be the same as the speciilc gravity of water, the effective length of the barometric leg 8 is changed by variation of the liquid level in the digester l. Ii the liquid level i the digester is at a level H, as indicated in Figure l, it is evident that the pressure exerted by a column of the liquid of the length H--A upon the low-pressure chamber will becounteracted and cancelled by the weight of the water in pipe 8 between the levels H and A. Thus, it can readily be seen that during the liquid level measuring operation the pressure in the low-pressure chamber l2 will always be less than the pressure in the high-pressure chamber I4 by an amount equal to the pressure exerted by a column of water of the height IIB, where- :by the instrument Il will indicate a maximum pressure diiierenti'al with the liquid level at the lower level A and a minimum or zero differential with the liquid level at the upper or reference level B For the convenience of the cooks. when applied to a sulphite digester; the instrument is preferably calibrated to read in inches of liquor level below the reference level B, i. e. inches from fthe top of the dlgester, so the instrument is set up to read zero inches for zero diiierential and maxi by the hydrostatic pressure oi' the lliquor" above point 2| and so an additional correction may be needed to the calibration in this range.

This

correction may be minimized by providing a condensing chamber Il of relatively large volume.

As many embodiments may be made of the above invention, and as many changes might be made in the embodiment above described, it is to .be understood that all matter hereinbei'ore set forth or shown in the accompanying drawings is to be interpreted as illustrative onlyand not in a limiting sense.

I claim:

l. In apparatus for measuring and recording.

the level of a liquid in a tank containing chemically active liquid and vapors, in combination, a differential pressure measuring and recording instrument of the manometer type having high and low pressure legs, one ot the legs having a lrelatively large cross-sectional area and anoat in said leg for operating a recording mechanism, first pipe means connecting the high pressure leg with said tank at a point near `the top thereof, second pipe means connecting'the other leg to said tankat a second point lowerdown thereon, said pipe means having a common connection with a water. supply, valve means in said pipe means for separately admitting fresh water to said respectivepipe means for ushing the same, means in said first pipe means interposed between said tank and said instrument providing a body .of liquid automatically maintained at a constant level to provide .a standard reference level for Ysaid instrument, and means in said second pipe meansinterposed between said tank and said instrument providing a relatively large lbody of water as a water seal to forestall migration of the chemically active liquid in said tank through said pipe means to said instrument due tomovement of liquid in said pipe means caused by changes in diierentlal pressure.

2. In apparatus for measuring and recording the level of a liquid in a tank containing chemically active liquid by means of a differential pressuremeasuring and vrecording instrument. having high and low pressure chambers, at least one of which being so constructed that a relatively large volume of liquid may be displaced from said chambers during operation or, said instrument, in combination, pipe means for connecting one chamber of. said instrument with said tank at la point near the top thereof and connecting the other chamber of said instrument to said tank at va. second point lower down thereon, said pipe means having connectionv with a supply of liquidv chemically inactive with respect posed thereto and lnotdisadv tageouslyallected by association with said chemically active liquid, and valve meansin said pipe means for admitting said inactive liquid to said pipe means to ilush the same, said pipe means being of such size as to hold a quantity of said inactive liquid sui'ilcient to forestall undesired migration of the chemically active liquid through said chemically inactive liquid to said instrument during the time when s'aid pipe means are not being ushed with said inactive liquid.

3. In apparatus for measuring and recording the level of a liquid in a tank containing chemi- 'to the parts'of said inst t which are ex-` from said chambers during operation of said instrument, in combination, pipe means for connecting one chamber of said instrument with said tank at a point near the top thereof and connecting the other chamber of said instrument to said tank at a second pointlower down thereon, said pipe means having connection with a supplyof liquid chemically inactive with respect to the parts of said instrument which are ex'- posed thereto and not disadvantageously. aiected by association with said chemically active liquid, valve means in said pipe means for admitting said inactive liquid to said pipe means,

I and means in said pipe means interposed between said tank and said instrument providingv relatively large body of said inactive liquid to forestall undesired migration of the chemically active' liquid through .said chemically inactive liquid to said instrument.

4. In apparatus for measuring and recording the level of a liquid in a tank containing chemically active liquid, in combination, a diil'erential pressure measuring. and recording instrument having high and lo'w pressure chambers, pipe means for connecting` one-chamber of said instrument with said tank at' a point near the top thereof and for 'connecting the other chamber of said instrument with said tank at a second point lower down thereon, said pipe means having connection with a supply of liquid chemically inactive with respect to the portions of.

said instrument which are exposed thereto and not disadvantageously affected by association with said chemically active liquid, at least one of said chambers o! said instrument being so constructed that a relatively large volume of liquid may move into and out of said chamber pressure measuring and recording instrument of the mercury manometer type having high and low pressure chambers, and 'a float in one of said chambers for operating a recording mechanism, nrst pipe means connecting the high pressure chamber witl said digester at a point near the top thereof, second pipe means connecting the other chamber to said digester at a second point lower down thereon, said pipe means having a common connection with the water supply,

at least one of said chambers of said instrument l having a relatively large cross-sectional area whereby a relatively large volume of liquid may move into and out of said chamber during operation of said instrument thus disturbing the water in said pipe means and causing migration ot the chemically active liquid from the tank toward the instrument, and valve means in said pipe means for separately admitting fresh water to said respective pipe means simultaneously for flushing the same to forestall said migration and to change the differential pressure on said instrument to record the ilushing operation.

' MALCOLM B. HALL, 

